Corrosion of Polycrystalline Fe-Si Alloys Studied by TMS, CEMS, and XPS

The high-temperature corrosion behavior of three polycrystalline Fe-Si alloys containing approximately 4, 5, and 10 at% Si was studied using transmission Mössbauer spectroscopy (TMS), conversion electron Mössbauer spectroscopy (CEMS), and x-ray photoelectron spectroscopy (XPS). The XPS measurements reveal the strong segregation process of silicon atoms to the surface. Moreover, the obtained XPS results suggest that the presence of adsorbed oxygen on the Fe-Si surface effectively enhances the silicon segregation process. On the other hand, the obtained TMS and CEMS spectra show that even 10% of silicon atoms dissolved in the iron matrix do not prevent high-temperature corrosion of the studied Fe-Si alloys. During exposure to air at 870 K, a systematic growth of an α-Fe₂O₃ compound was observed. Finally, the Mössbauer results show that, during exposure to air, oxygen atoms diffuse to the studied polycrystalline materials not only through the oxide/metal interface on the surface but also along the grain boundaries. Such effects result in the formation of iron oxides in deeper parts of the alloy.